The present invention relates to a metallic holder device provided with blind holes for the partial heat treatment of work tools having a work area and a clamping area in furnaces with homogeneous distribution of heat in the furnace interior, especially for vacuum batch furnaces with compressed-gas quenching.
Drills, milling machine cutters, reamers and similar well known work tools are customarily formed having a clamping area, by which they are fastened in the machine tool chucks and a work area with which the machining or cutting steps are carried out. As a result of the different requirements placed on these areas of the work tool body, the work tools must also exhibit different properties in the respective regions; such as for example strengths. These work tools can therefore be manufactured from two different materials or the two areas of the work tool can be subjected to a differing heat treatment. It is necessary in the case of a unified material to use partial heat treatments which harden only the work area, whereby a longer service life is obtained; the clamping area on the other hand should retain the original technical properties of the material as much as possible. DE-OS 31 11 218 discloses a furnace for the partial heat treatment of tools which exhibit a work area and a clamping area. To this end, the clamping area of the tools is fastened in a holder which is insulated and absorbes a certain amount of calorific energy during the heat treatment so that only the work area is heated over the material-specific transformation temperature and subsequently quenched whereas the clamping area remains at an essentially constant temperature level during the heat treatment and the quenching treatment. To this end, the tools are inserted by their clamping area into boreholes of the plate-like holder which are insulated from the furnace area and are cooled from below.
This furnace has the disadvantage that considerable temperature differences necessarily occur during the heating and the quenching between the work area and the clamping area of the tools which can result in different states of stress in the material and to changes in dimension and form.
DE-OS 33 13 651 corresponding to U.S. Pat. No. 4,682,011 describes a furnace for the partial heat treatment of tools in which the holders are integrated into a plate of heat-insulating material which subdivides the work space of the furnace into two separate heating areas which, for their part, can be heated via separable heating elements to different levels. Thus, special furnaces are required here with movable connecting members between the individual heating elements.